Blow molding products, such as household and industrial containers (for example, plastic food bottles for milk, juice, and water; chemical bottles for detergent and motor oil; and heavy-duty storage drums) have high performance and appearance standards. Blow molding products are typically formed using existing commercial equipment and existing blow molding processing techniques, with no, or minimal, equipment modifications. In addition, fabricators seek to minimize the cycle time to produce a product, and thus increased cycle times are disfavored. Customer requirements for blow molding resins include product consistency, good processability, adequate resin swell, and an optimum balance of top load (stiffness, modulus), environmental stress crack resistance (ESCR) and impact resistance.
Improved resin stiffness will increase the load bearing capacity of blow-molded containers. Thus, light weight blow-molded containers with increased stiffness can be used to replace heavier metal containers. In addition, such lighter weight containers can be stacked more efficiently, resulting in more efficient use of storage space and transportation space.
Environmental stress crack resistance (ESCR) is a measure of the susceptibility of a resin to mechanical failure by cracking. Poor environmental stress crack resistance of high density ethylene polymer, blow molded articles, such as blow molded containers for household and industrial goods, has impeded the use of these containers for such goods. Due to insufficient ESCR, blow molded containers, fabricated from high-density ethylene polymer, may crack before or during storage.
Impact resistance is a measure of the ductility of a container. Containers with poor impact strength will crack or fracture upon being struck by a high force or when dropped from a high elevation. Insufficient impact resistance results in a blow molded container that is too brittle for conventional use.
U.S. Pat. No. 6,194,520 discloses high molecular weight, high density ethylene polymer blends capable of being blow molded, and with excellent processability. The blends have a density of at least about 0.930 g/cc, a flow index (I21) of at least about 2 g/10 min, a melt flow ratio (MFR) of at least about 60, and a polydispersity index of at least about 8. The blends contain at least about 0.3 weight fraction of a relatively high molecular weight (HMW) component having a density of at least about 0.900 g/cc, a flow index or high load melt index (I21) of at least about 0.2 g/10 min, and a flow ratio (FR) at least about 10; and a relatively low molecular weight (LMW) component having a density of at least about 0.930 g/cc, and a melt index (I2) no greater than about 1000 g/10 min.
U.S. Pat. No. 6,316,546 (see also U.S. Pat. No. 6,458,911) discloses relatively high molecular weight, high density ethylene polymers (HMW-HDPE) capable of being formed into thin films of high strength. Such polymers having a density of at least about 0.925 g/cc, a flow index (I21) no higher than about 15 g/10 min, a melt flow ratio (MFR) of at least about 65, and a dynamic elasticity at 0.1 rad./sec of no higher than about 0.7, at a corresponding complex viscosity at 0.1 rad/sec no higher than about 14E5 (14×105 poises). The ethylene polymer is a bimodal blend of relatively high molecular weight (HMW) and low molecular weight (LMW) ethylene polymer.
European Patent 1169388B1 (see also WO 00/60001 and U.S. Pat. No. 6,433,095) discloses a high density multimodal polyethylene, having a shear ratio (SR) of 18 or more, and comprising at least 20 weight percent of a high molecular weight fraction, which has a density (ρ) of 0.930 g/cm3 or less, and a high load melt index (HLMI) of 0.30 g/10 min or less.
International Publication No. WO 2004/048468 discloses a polyethylene composition comprising 20 to 50 weight percent of a copolymer of ethylene and a C3-C20 alpha-olefin comonomer, and 50 to 80 weight percent of a lower weight average molecular weight ethylene polymer, and where the polyethylenes of the composition together have a density of 935 to 965 kg/m3, a weight average molecular weight of 60,000 to 300,000 g/mol, an MFR2.16, at 190° C., of 0.1 to 10 g/10 min, and a molecular weight distribution (MWD) from 2.5 to 20. The copolymer has a comonomer content of from 0.006 to 9 mole percent, and a degree of branching of 0.03 to 45 branches per 1000 carbons. The ethylene polymer has a density of 939 to 975 kg/m3, and a weight average molecular weight of 20,000 to 200,000 g/mol.
European Application No. 1201713A1 discloses a polyethylene resin comprising a blend from 35 to 49 weight percent of a first polyethylene fraction of high molecular weight, and 51 to 65 weight percent of a second polyethylene fraction of low molecular weight. The first polyethylene fraction comprises a linear low density polyethylene having a density of up to 0.928 g/cm3, and an HLMI of less than 0.6 g/10 min, and the second polyethylene fraction comprises a high density polyethylene having a density of at least 0.969 g/cm3, and an MI2 of greater than 100 g/10 min. The polyethylene resin has a density of greater than 0.951 g/cm3, and an HLMI of from 1 to 100 g/10 min.
U.S. Publication No. 2004/0266966 discloses a polyethylene resin having a multimodal molecular weight distribution, and a density in the range from 0.925 g/ccm to 0.950 g/ccm, a melt index (I2) in the range from 0.05 g/10 min to 5 g/10 min. The polyolefin resin comprises at least one high molecular weight (HMW) ethylene interpolymer and at least a low molecular weight (LMW) ethylene polymer.
U.S. Publication No. 2004/0034169 discloses a polymer composition comprising a low-molecular-weight (LMW) ethylene polymer component and a high-molecular-weight (HMW) ethylene polymer component. Preferably, the LMW polyethylene component and the HMW polyethylene component co-crystallize in the composition such that it exhibits a single peak, or substantially single peak, in a lamella thickness distribution (“LTD”) curve. The ethylene polymer for the LMW and the HMW polyethylene components can be either homopolyethylene or ethylene copolymer. Preferably, both components are an ethylene copolymer of the same or different composition (that is, with the same or different comonomers).
U.S. Pat. No. 7,166,676 (see also U.S. Publication No. 2003/0055176) discloses a process for the preparation of blends, including an ethylene copolymer, by copolymerizing ethylene and at least one comonomer, selected from a compound represented by the formula H2C═CHR, wherein R is an alkyl group or an aryl group, or a diene, in the presence of a solid catalyst system comprising a support, a transition metal compound and an activator capable of converting the transition metal compound.
European Patent No. 1093658B1 discloses an insulating composition for communication cables, which a multimodal olefin polymer mixture, obtained by polymerization of at least one α-olefin, in more than one stage, and having a density of about 0.920-0.965 g/cm3, a melt flow rate (MFR2) of about 0.2-5 g/10 min an FRR21/2≧60, and an environmental stress cracking resistance (ESCR), according to ASTM D 1693 (A/10 percent Igepal), of at least 500 hours. The olefin polymer mixture comprises at least a first and a second olefin polymer, of which the first is selected from (a) a low molecular weight olefin polymer with a density of about 0.925-0.975 g/cm3, and a melt flow rate (MFR2) of about 300-20 000 g/10 min, and (b) a high molecular weight olefin polymer with a density of about 0.880-0.950 g/cm3, and a melt flow rate (MFR21) of about 0.5-20 g/10 min.
European Patent Application No. 1359192A1 discloses a polyethylene resin comprising from 44 to 55 weight percent of a high molecular weight polyethylene fraction, and from 45 to 56 weight percent of a low molecular weight polyethylene fraction. The high molecular weight polyethylene fraction comprises a linear low density polyethylene having a density from 0.913 to 0.923 g/cm3, and an HLMI from 0.02 to 0.2 g/10 min; and the low molecular weight polyethylene fraction comprises a high density polyethylene having a density of at least 0.969 g/cm3, and an MI2 of greater than 100 g/10 min.
U.S. Pat. No. 4,461,873 (see also EP0100843B1) discloses ethylene polymer blends of a high molecular weight ethylene polymer, preferably an ethylene-mono-1-olefin copolymer, and a low molecular weight ethylene polymer, preferably an ethylene homopolymer, both preferably with narrow molecular weight distribution and low levels of long chain branching. These resins are useful for the manufacture of film or in blow molding techniques, and the production of pipes and wire coating.
U.S. Pat. No. 6,946,521 discloses a polyethylene resin comprising from 35 to 49 weight percent of a first polyethylene fraction of high molecular weight, and from 51 to 65 weight percent of a second polyethylene fraction of low molecular weight. The first polyethylene having a density of up to 0.930 g/cm3, and an HLMI of less than 0.6 g/10 min, and the second polyethylene fraction comprising a high density polyethylene having a density of at least 0.969 g/cm3, and an MI2 of greater than 10 g/10 min, and the polyethylene resin, having a density of greater than 0.946 g/cm3, an HLMI from 1 to 100 g/10 min, a dynamical viscosity, measured at 0.01 radians/second, greater than 200,000 Pa·s, and a ratio of the dynamical viscosities, measured at, respectively 0.01 and 1 radians/second, greater than 8.
International Publication No. WO 2005/103100 discloses a polyethylene, which comprises ethylene homopolymers and copolymers of ethylene with alpha-olefins, and has a molar mass distribution width, MW/M, from 6 to 100; a density from 0.89 to 0.97 g/cm3; a weight average molar mass, MM, from 5,000 g/mol to 700,000 g/mol, and has from 0.01 to 20 branches/1000 carbon atoms, and at least 0.5 vinyl groups/1000 carbon atoms. From 5-50 weight percent of the polyethylene having the lowest molar masses have a degree of branching of less than 10 branches/1000 carbon atoms, and from 5-50 weight percent of the polyethylene having the highest molar masses have a degree of branching of more than 2 branches/1000 carbon atoms.
International Publication No. 2001/14122 (see also EP1204523B1) discloses a bimodal HDPE for the production, by blow molding, of medium to large volume containers having improved environmental stress crack resistance. The bimodal HDPE is disclosed as preferably having a density of 940 to 970 kg/m3, a weight average molecular weight of 200,000 to 450,000 D, a number average molecular weight of 6,000 to 20,000 D, a molecular weight distribution of 15 to 55, a MFR21 of 2 to 12 g/10 min, a tensile modulus at least 900 mPa, and a comonomer content of 0.5 to 10 weight percent.
European Patent Application No. 1333040A2 discloses a polyolefin comprising a high molecular weight component (HMW) and a low molecular weight component (LMW), the LMW component forming 20 to 80 weight percent of the polyolefin, and the HMW component forming 15 to 75 weight percent of the polyolefin, and having an Mw/Mn of less than 10. The polyolefin has a melt strength greater than [0.024×(20,000+η0.05)0.5]−2.6 (where η0.05 is the melt viscosity (Ns/m2) at a shear rate of 0.05 s−1); and the ratio of peak molecular weight of the high MW component over that of the low MW component is above 2.
European Patent Application No. 1319685A1 discloses a process for the preparation of polyethylene resins having a multimodal molecular weight distribution that comprises the steps of: (i) providing a first high molecular weight, metallocene-produced, linear low density polyethylene (mLLDPE) resin having a density from 0.920 to 0.940 g/cm3, and a HLMI from 0.05 to 2 g/10 min; (ii) providing a second high density polyethylene (HDPE), prepared either with a Ziegler-Natta or with a chromium based catalyst, said polyethylene having a density ranging from 0.950 to 0.970 g/cm3, and a HLMI from 5 to 100 g/10 min; (iii) physically blending together the first and second polyethylenes to form a polyethylene resin having a semi-high molecular weight, a broad or multimodal molecular weight distribution, a density ranging from 0.948 to 0.958 g/cm3, and a HLMI from 2 to 20 g/10 min.
U.S. Pat. No. 6,749,914 discloses a melt blended HDPE for pipe and fitting material, and which has a density in the range of 0.945 to 0.955 g/cc, values of melt flow index, according to ASTM D1238, less than 0.4, and has enhanced physical properties and process characteristics.
U.S. Pat. No. 4,525,322 disclose polyethylene blends for blow molding processes, and which comprise from 12 to 25 weight percent of a high molecular weight component, 5 to 83 weight percent of a medium molecular weight component, and 5 to 83 weight percent of the low molecular weight component. The ratio of high molecular weight to medium molecular weight is greater than, or equal to, 1.7, and the ratio of medium molecular weight to low molecular weight is greater than, or equal to, 1.7, and the blend has a melt index in the range of 0.01 to 2.0.
International Publication No. WO 00/18813 discloses a process for the preparation of polyethylene resins having a multimodal molecular weight distribution, and which process comprises: (i) contacting ethylene monomer and a comonomer, comprising an alpha-olefin having from 3 to 10 carbon atoms, with a first catalyst system in a first reactor, under first polymerization conditions in a slurry process, to produce a first polyethylene having a first molecular weight an HLMI of not more than 0.5 g/10 min, and a first density of not more than 0.925 g/ml; (ii) providing a second polyethylene having a second lower molecular weight and higher density than the first polyethylene; and (iii) mixing together the first and second polyethylenes to form a polyethylene resin having a multimodal molecular weight distribution.
Japanese JP2001226496A (Abstract) discloses a polyethylene resin sheet obtained from a resin composition comprising 98-55 weight percent of an ethylene homopolymer or ethylene-α-olefin copolymer having 0.93-0.97 g/cm3 density, and 2-45 weight percent of an ethylene copolymer satisfying requirements of a 0.86-0.94 g/cm3 density, 0.01-50 g/10 min melt flow rate, and 1.5-4.5 molecular weight distribution (Mw/Mn).
International Publication No. WO 2004/016688 discloses a polyethylene composition that has a density of 0.945 to 0.960 g/cc, and a melt flow index of 0.1 to 0.4. The composition is a melt blend of a linear low density polyethylene resin and/or a linear medium low density polyethylene resin, and a high density polyethylene resin.
International Publication No. WO 95/11264 discloses resins which are in situ catalytically produced blends of ethylene resins of broad bimodal molecular weight distribution. The resins of the invention are characterized by a blend of low molecular weight component and high molecular weight component. The resin has a molecular weight distribution, which is characterized as MFR or Mw/Mn. The bimodal molecular weight resins are disclosed as being able to be processed into films on existing equipment, and exhibit good processability in blown film production and provide film product of excellent FQR.
Additional polyethylene-based compositions are disclosed in U.S. Pat. No. 6,809,154; U.S. Pat. No. 4,617,352; U.S. Pat. No. 6,541,581; U.S. Pat. No. 6,090,893; U.S. Pat. No. 5,310,834; U.S. Pat. No. 6,649,698; U.S. Pat. No. 4,603,173; U.S. Pat. No. 7,129,296, U.S. Pat. No. 5,688,865; U.S. Publication No. 2005/0288443; U.S. Publication No. 2003/0149181; International Publication No. WO 2004/058878; International Publication No. WO 2004/058877; International Publication No. WO 2004/058876; International Publication No. WO 99/65039; and International Publication No. WO 01/79344 (see also EP1146077A); International Publication No. WO 2005/121239; International Publication No. WO 96/18677; International Publication No. WO 2004/007610; International Publication No. WO 01/14122; European Application No. 1384751A1; European Application No. 1595897A1; and European Application No. 0717055A2.
However, there remains a need for polyolefin compositions that can provide an optimized balance of stiffness, stress crack and impact resistance. This need is particularly pronounced in the fabrication of blow molded household and industrial containers, and especially in the area of reduced resin, light-weight, rigid containers. Some of these and other issues are satisfied by the following invention.